This invention relates to a method for IMS (Internet Protocol Multimedia Subsystem) support for enterprise PBX (Private Branch Exchange) user roaming, originations and terminations. While the invention is particularly directed to the art of telecommunications, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications.
By way of background, there has been considerable work done in TISPAN (Telecoms & Internet converged Services & Protocols for Advanced Networks) and 3GPP (3rd Generation Partnership Project) to specify how to support NGCN (Next Generation Corporate Network) users within an NGN (Next Generation Network). An NGN is an operator network based on IMS. Each NGCN is comprised of one or more IP (Internet Protocol) PBX systems with IP interconnect to an NGN, which is normally referred to as business trunking or SIP trunking.
Currently, there are two NGCN/NGN interconnect models—the subscription model and the peering model. In the subscription model, the NGCN interconnects to the NGN via the Gm reference point (a SIP-based reference point normally shown between the user equipment (UE) and the Proxy-Call Session Control Function (P-CSCF)). The NGCN registers into the NGN on behalf of all NGCN users, which receive some services from their NGCN as well as receiving other services from the NGN IMS (IP Multimedia Subsystem) according to the provisioned application servers and filter criteria. The subscription model clearly defines how the NGN provides basic call originating and terminating services plus enhanced originating and terminating services to the NGCN users. There is currently no agreed standard for how the NGN in the subscription model provides roaming service to an NGCN user. In the peering model, the NGCN interconnects to the NGN via an inter-IMS interface (typically via an Interconnect Border Control Function (IBCF)) but does not register into the NGN on behalf of its users. The peering model clearly defines how the NGN provides basic transivrouting services for SIP requests originating in the NGCN. There is currently no agreed standard for how the NGN in the peering model provides basic terminating service, enhanced originating or terminating services, or roaming service to an NGCN user.
It is evident that there is a need for the NGN to provide various capabilities, including (1) basic call terminating service in the peering model, (2) enhanced terminating services in the peering model, (3) enhanced originating services in the peering model, and (4) roaming service in the subscription and peering models. The existing solutions and limitations are described generally below.
(1) The NGN interconnected to an NGCN in the peering model is defined as the trunking home NGN. The trunking home NGN is configured as the initial destination for all terminating requests to an NGCN user. The trunking home NGN receiving a request for an NGCN user must somehow retarget terminating SIP requests to the NGCN. The originating network forwards a SIP request to the trunking home NGN as a result of the DNS (Domain Name System) query, which identifies the trunking home NGN as the target for the request. Since the NGCN does not register on behalf of its users with the NGN in the peering model, it is unclear how the NGN can retarget the request to the NGCN. Existing approaches involve the use of SIP proxies to retarget such a request to the NGCN based on provisioned data.
Another possibility is to configure a private DNS within the NGN to retarget the request to the NGCN. Neither approach scales well if there are a significant number of interconnected NGCNs. Either way, the NGN must have special routing procedures and provision special routing data for each NGCN interconnection. It would be preferable if the IMS NGN could instead use generic IMS procedures driven by provisioned subscriber data to perform the request retargeting in an easily scalable manner.
(2) To provide enhanced terminating services in the peering model, in addition to the procedure in item 1 above, the NGN would have to also provision a special application server in the routing path of terminating requests to provide enhanced services for these requests. So at least two entities would need to be provisioned on the routing path for each NGCN interconnection. Since fixed application servers would need to be allocated to provide these terminating services, it is difficult to reuse application servers interconnected via standard IMS interfaces, and there is less ability to assign traffic to application servers as usage and the number of interconnected NGCNs grows.
(3) By configuring the trunking home NGN as the next destination for all originating requests from the NGCN in the peering model, the NGN can provide basic transit/routing services to the NGCN user. But to provide enhanced originating services to this NGCN user, the NGN would have to also provision a special application server in the routing path of originating requests to provide enhanced services for these requests. Since fixed application servers would need to be allocated to provide these originating services, it is difficult to reuse application servers interconnected via standard IMS interfaces, and there is less ability to assign traffic to application servers as usage and the number of interconnected NGCNs grows.
(4) For roaming NGCN users, the visited NGN is defined as the network into which the NGCN user is roaming, and to which the NGCN user is directly connected. When attempting to register for service, the NGCN user sends its registration request via the visited NGN to the registrar name provisioned in the device. The roaming home NGN is defined as the registrar for the NGCN user and the network to which registration requests from the NGCN user are first routed by the visited NGN. The visited NGN forwards a SIP registration request to the roaming home NGN as a result of DNS, which identifies the roaming home NGN as the SIP registrar. Analogously to item 1 above, the roaming home NGN must somehow retarget SIP registration requests to the NGCN to gain access to services provided by the NGCN. Existing approaches to forwarding the SIP registration request from the roaming home NGN to the NGCN involve the use of SIP proxies to retarget such a request to the NGCN based on provisioned data. Another possibility is to configure a private DNS within the NGN to retarget the request to the NGCN. Neither approach scales well if there are a significant number of interconnected NGCNs. Either way, the NGN must have special routing procedures and provision special routing data for each NGCN interconnection. It would be preferable if the IMS NGN could instead use generic IMS procedures driven by provisioned subscriber data to perform the request retargeting in an easily scalable manner. If the NGCN also registers on behalf of its users to the trunking home NGN, as in the subscription model, it is also not clear how to distinguish between registration requests from the visited NGN and the NGCN.
The present invention contemplates a new and improved method that resolves the above-referenced difficulties and others.